1. Field of the Invention
The present invention relates to a novel method for preparing N,N-disubstituted hydroxylamine compounds which are useful as developing agents of silver halide photosensitive materials and additives for polymers.
2. Related Art
N,N-Dialkylhydroxylamine compounds are know to have suitable capabilities for developing agents of silver halide photosensitive materials as described in Japanese Patent Publication (KOKOKU) No. (Sho) 42-2794/1967. On the basis of the excellent capabilities, they have been widely and practically used as diffusion transfer-type developers in recent years. N,N-Dialkylhydroxylamine compounds are also useful as process stabilizers for polyolefin compositions in the presence of auxiliary stabilizing agents such as phenolic antioxidants (U.S. Pat. No. 4,590,231), and useful as stabilizer for arylene sulfide resins utilizing antioxidants based on phenolic amides or esters (U.S. Pat. No. 4,464,122).
Several methods for preparing N,N-dialkylhydroxylamine compounds have been known so far. U.S. Pat. No. 3,293,034 and Japanese Patent Publication (KOKAI) No. (Sho) 42-2794/1967 disclose methods for preparing N,N-dialkylhydroxylamine compounds which comprises the step of oxidizing dialkylamine compounds by using hydrogen peroxide. However, these methods are not preferred because they can achieve only a poor yield and the reactions entail a temperature of 50 to 60.degree. C., which involves risk of explosion.
U.S. Pat. No. 3,655,764 discloses a method for preparing N,N-dialkylhydroxylamine compounds by oxidizing dialkylamine compounds using hydrogen peroxide, which includes the addition of a chelating agent such as ethylenediaminetetraacetic acid (EDTA). U.S. Pat. No. 3,661,996 discloses a method for purifying a resulting N,N-dialkylhydroxylamine compound by means of a special apparatus which utilizes a strongly acidic ion exchange resin. However, both methods have several problems, e.g., they only give an insufficient yield of approximately 50%, and the latter method requires the special apparatus.
U.S. Pat. No. 3,491,151 discloses a method for preparing N,N-dialkylhydroxylamine compounds by allowing hydroxylamines react with alkyl halides, alkyl tosylates or the like. However, this method is also undesirable, because it requires a prolonged reaction time and achieves a yield of no more than about 50%. Tetrahedron Letters, Vol. 37, No. 33 pp. 6025-6028, 1996 discloses a method for synthesizing nitrone compounds by oxidizing dibenzylamine by means of a combination of aqueous hydrogen peroxide and methyltrioxorhenium. According to this synthetic method, an N,N-dibenzylhydroxyl-amine compound is produced in addition to a nitrone compound as a major product. However, its yield is low. Furthermore, the method requires a large amount of methyltrioxorhenium. For these reasons, the method is only disadvantageously applied to practical preparations of N,N-dibenzylhydroxylamine compounds.
Japanese Patent No. 2,567,656 discloses a method comprising the steps of first synthesizing a tertiary amine compound, and then treating the resulting tertiary amine compound with aqueous hydrogen peroxide to form an N-oxide compound, followed by producing an N,N-dialkylhydroxylamine compound according to the reverse Michael reaction. However, this method involves a lot of reaction steps because it needs the preparation of the tertiary amine compound. The method is also disadvantageous from a viewpoint of safety, because it requires a high concentration of aqueous hydrogen peroxide. Further method is proposed which comprises addition of a secondary amine compound to a reaction system containing hydrogen peroxide together with a rhenium catalyst (Tetrahedron Letters, Vol. 37, No. 33, pp. 6025-6028, 1996). However, this method has a problem in that a desired N,N-dialkylhydroxylamine compound can hardly be obtained.
An object of the present invention is to provide a method for preparing N,N-disubstituted hydroxylamine compounds. More specifically, the object is to provide a method that enables the preparation of the desired compounds in a high yield by applying a safe and simple reaction step. Another object of the present invention is to provide a method for preparing N,N-disubstituted hydroxylamine compounds which enables, in addition to the aforementioned characteristic features, isolation and purification of the desired compounds without using any special purification apparatuses.